1. Field of the Invention
The present invention relates to a controlled switching device controlling opening and closing timing of a power switchgear such as a circuit breaker, and more particularly to a controlled switching device, which suppresses an overvoltage generated in time of making of a transmission line.
2. Description of the Related Art
In a conventional controlled switching device, the device finds frequencies, phases, and amplitudes from a power source voltage of a breaker and from measured waveforms of a load voltage for functional approximation; synthesizes an interpole voltage from the current time on using these approximation functions; executes a signal conversion based on a pre-arc characteristic of the breaker and a signal conversion based on variations of a mechanical action of the breaker; and determines a target closing time thereof (for example, see Patent Document 1). Then, the breaker is closed at this target closing time, thus suppressing the overvoltage generated at the time of making of a transmission line.
Patent Document 1: JP-A2003-168335
In general, sometimes a controlled switching device is used for a high-speed reclosing path in the event of a breakdown of a transmission line. In such a usage, it is required that within the limited time of about 500 milliseconds from the occurrence of a failure of the transmission line, a target closing time, at which the overvoltage is suppressed in time of making of the transmission line, and then the breaker is closed. In the above-described conventional controlled switching device, a lot of calculations have to be made to determine the target closing time during working of the device. Consequently, there has been demand for a high-performance arithmetic unit, with increased the cost of the device.